Today, sprinklers are often used for automatic water spraying and irrigating. The sprinkler is usually coupled with the water source, and the water strikes an arm of a swing unit of the sprinkler to achieve the goal of water spraying. The swing unit usually has a spring, so when the arm of the swing unit is struck by water, it can restore using the resilient force provided by the spring and obtain a circular spraying area to further achieve the goal of irrigation. However, conventional sprinklers may have the following drawbacks: (a) the swing unit of the conventional sprinkler uses the resilient force provided by the spring to restore, and is struck by water to spray. However, the spring has an elastic coefficient, and it is difficult t o adjust the tightness through the sprinkler, so the rebounding speed of the swing unit cannot be enhanced by rewinding the spring, and the spraying cannot be concentrated after the swing unit is struck by water. If the water is sprayed to an area with concentrated planting, the water cannot be averagely and effectively distributed to the plants in the area; and (b) the spring in the conventional sprinkler is easily to become fatigue after being used for a certain period of time, so the rebounding speed of the swing unit is reduced, and the speed cannot be increased after the swing unit is struck by water, so that the water cannot precisely strike the swing unit to cause uneven and ineffective water spraying. If the user wants to fix the problem, he/she has to uninstall the sprinkler to replace the spring or replace the sprinkler, which is inconvenient and not cost-effective.